This invention relates generally to disconnect switches, and, more particularly, to fused disconnect switches.
Fuses are widely used as overcurrent protection devices to prevent costly damage to electrical circuits. Fuse terminals typically form an electrical connection between an electrical power source and an electrical component or a combination of components arranged in an electrical circuit. One or more fusible links or elements, or a fuse element assembly, is connected between the fuse terminals, so that when electrical current through the fuse exceeds a predetermined limit, the fusible elements melt and opens one or more circuits through the fuse to prevent electrical component damage.
In some applications, fuses are employed not only to provide fused electrical connections but also for connection and disconnection, or switching, purposes to complete or break an electrical connection or connections. As such, an electrical circuit is completed or broken through conductive portions of the fuse, thereby energizing or de-energizing the associated circuitry. Typically, the fuse is housed in a fuse holder having terminals that are electrically coupled to desired circuitry. When conductive portions of the fuse, such as fuse blades, terminals, or ferrules, are engaged to the fuse holder terminals, an electrical circuit is completed through the fuse, and when conductive portions of the fuse are disengaged from the fuse holder terminals, the electrical circuit through the fuse is broken. Therefore, by inserting and removing the fuse to and from the fuse holder terminals, a fused disconnect switch is realized.
Known fused disconnect switches of this type, however, are disadvantaged in certain applications. For instance, in telecommunications applications, increasing power demands of equipment loads have rendered many fused disconnect switches inadequate. More specifically, known fused disconnect switches having adequate ratings (e.g., capable or interrupting 20 kA at 80 VDC) are relatively large and difficult to mount in telecommunication panel system, and ganging conventional disconnect switches on a common input bus in a telecommunications system is difficult, if not impossible Still further, especially when a large number of disconnect switches are employed, quick and accurate identification of opened fuses is necessary so that opened fuses may be identified and replaced. Conventional fused state identification mechanisms are not as reliable as desired for telecommunications applications.
For at least the above reasons, use of known fused disconnect switches have not completely met the needs of certain end applications, such as use in telecommunications systems.
In an exemplary embodiment, a fused disconnect switch assembly includes a switch housing assembly and a pull out fuse assembly. The switch housing assembly includes a housing defining a fuse receptacle, first and second terminal contacts within the housing and located adjacent the fuse receptacle, and an alarm terminal extending from the fuse receptacle to an exterior of the fuse housing. The pull out fuse assembly includes a housing, a line side terminal extending from the housing, a load side terminal extending from the housing, and a primary fuse having first and second conductive end caps. The fuse end caps are coupled to respective line side and load side terminals of the pull out fuse assembly housing, and the first and second terminal contacts of the switch housing assembly receive the load side and the line side terminal blades of the pull out fuse assembly. An electrical connection is therefore established between the fuse assembly and the switch housing assembly when the fuse assembly is inserted into the fuse receptacle of the switch housing assembly, and the electrical connection is broken, as desired, by removing the fuse assembly from the fuse receptacle of the switch housing assembly.
More specifically, the fuse assembly includes a fuse terminal assembly having upper and lower fuse brackets. A primary fuse and a secondary indication fuse are coupled to the fuse brackets and mounted in parallel therebetween. Line side and load side terminals extend from the respective fuse brackets for connection to terminal contacts in the switch housing assembly. The secondary fuse includes a fuse indicator cap that completes an electrical connection with a first lead of an LED mounted in the housing when the primary fuse is opened. A second lead of the LED is coupled to a fuse alarm terminal, also mounted in the fuse assembly housing. The fuse alarm terminal is accessible through an opening in the fuse assembly housing, and the alarm terminal of the switch housing assembly engages the fuse alarm terminal when the fuse assembly is inserted into the fuse receptacle. Local fuse state indication is therefore provided with the LED in the fuse assembly housing, and remote fuse state identification is facilitated with a signal transmitted through the fuse alarm terminal and the switch housing assembly alarm terminal. When the primary fuse is opened, the LED is illuminated and an alarm signal is transmitted through the alarm terminals.
The switch assembly housing, in one embodiment, includes a groove in one side to facilitate panel mounting, and a threaded nut on the other side to secure the switch assembly housing to the panel when the groove is engaged to an edge of a panel cutout. Thus, panel mounting of the fused disconnect switch is not only facilitated but simplified for relatively quick and easy installation in the field. In a further embodiment, at least one terminal extends from the switch assembly housing and includes a threaded nut for mounting to a common bus connection with a fastener. Moreover, the fused disconnect switch housing is sized and dimensioned to permit multiple fused disconnects switches to be ganged together and mounted to a common bus bar.
A fused disconnect switch is therefore provided that is advantageous for use, in for, example, paneled telecommunications systems.